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Ion Motion Through an RFQ
Varying the q-value Varying the Buffer Gas Pressure The q-value We define the q-value for an ion inside an RFQ device to be: Where: e = the charge on the ion Vpp = the peak-to-peak voltage applied to the RFQ m = the mass of the ion r0 = the radius of the RFQ Ω = the angular frequency of the applied RF-field The q-value governs the stability of the ions paths in the RFQ. In an RFQ the ion motion is stable for q ≤ For q-values higher than the ion motion is unstable and hence the ions are not trapped.
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The Effect of Varying the q-value
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Buffer Gas Cooling An ion beam can be cooled via collisions with an inert buffer gas however such collisions cause the beam to diverge. The RFQ provides a force that pushes the ions onto its Z-axis hence an ion beam can be cooled inside an RFQ via collisions with a buffer gas without the beam diverging. By varying the buffer gas pressure one can control the time it takes for cooling to take place.
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The Effect of Varying the Buffer Gas Pressure
q=0.4_p=1^-2 q=0.4_p=1^-3 q=0.4_p=2.5^-2 q=0.4_p=5^-2 q=0.4_p=5^-3
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